Electrolytic electrocopying method and apparatus



Feb. 21; 1967 A. J. SMITH ET AL 3,305,459 ELECTROLYTIC ELECTROCOPYING METHOD AND APPARATUS Filed Aug. 27, 1963 INVENTORS 4; A/VJ 5/14/ 7/1 United States Patent 3,305,459 ELECTRULYTIC ELECTROCOPYING METHOD AND APPARATUS Alan J. Smith, Elmwood, Wis, and Jack K. Warren, Marine on St. Croix, Minn., assignors to Minnesota Mining and Manufacturing Company, St. Paul, Mind, a corporation of Delaware Filed Aug. 27, 1963, Ser. No. 304,823 7 Claims. (Cl. 204-48) This invention relates to an apparatus for the development of latent images imparted to a photosensitive copy paper. More particularly, this invention relates to a developing apparatus for electrolytic deposition from an electrolyte onto the photoconductive coating of a photosensitive copy paper to form a permanent visible image on said paper.

In the past, the electrolytic solution has been applied to the copy sheet or paper by a gelatin surfaced roller or a brush brought into contact with the photoconductive coating of the copy paper. Devices of this type are disclosed in US. Patent No. 3,011,963 to Johnson and Neher which is assigned to the assignee of this patent. Contact between the mechanical applicator of the electrolytic liquid solution and .the photoconductive coating of the copy paper has caused objectionable streaks and pinholing on the copy. Pinholing results where there is a flow in the coating or where the contact between the applicator and paper has caused abrasion of the coating and a low resistance current path is present in said areas. This abrasion is especially evident if the applicator is driven at a speed exceeding the lineal speed of the paper. In either instance, the poorly coatedor abraded areas cause an excessive current flow through said areas. This current flow is believed to partially burn the coating and the backing and is believed to create an excessive electrolytic deposition in said areas causing undesirable black spots or pinholing on the copy in the image areas or background rather than the desired controlled deposition on only the electrically conductive image areas. This pinholing in the background areas is objectionable and degrades the quality of the resulting print. The application of the electrolytic solution to the copy paper by means of a roller, having a sponge-like or fabric covering, which is driven by contact with the paper further results in a diminution in the quality of the image reproduced because an insufficient quantity of the electrolytic solution is made available at the surface of the exposed paper to propertly develop the image. Additionally, contact between the applicator of the electrolytic solution and the copy paper causes the image to bear streaks resulting from the uneven application of the solution over the exposed image area.

Therefore, a definite problem has existed and a new technique for the application of the electrolytic solution to the copy paper has been sought. A technique which would not require immersion of the sheet, or contacting the photosensitive coating in any manner by a mechanical applicator and which would still supply sutficient ions of the electrolytic solution to the co-py sheet to give an image having the density and image quality desired, has been the objective.

The present invention solves the aforementioned problem and has as one of its advantages the ability to supply a sufficient quantity of the electrolytic solution to a large area of the copy sheet in the presence of an electric current and with suflicient turbulence to uniformly plate the exposed image pattern and to minimize adverse effects in the background areas.

The present invention has as a further advantage the elimination of contact between the copy paper and the mechanical means supplying electrolytic solution to the copy paper.

The desired control of the electrolytic deposition is obtained through the use of an apparatus which will lift the electrolytic solution into contact with the copy paper in the presence of uniform electrical current, which apparatus in the illustrated embodiment comprises insulating rollers adapted to be at least partially immersed in the solution and spaced from the path of the copy paper and an electrode disposed in the solution.

These and other advantages will become more apparent as this description proceeds which refers to the accom panying drawing wherein:

FIGURE 1 is a diagrammatic view, partially in cross section, of a developer apparatus constructed in accordance with the present invention; and

FIGURE 2 is a diagrammatic side view, having portions broken away, of an optical inspector including an electrocopying device.

The use of electrolytic electrocopying of information stored in the form of microfilm copies is becoming increasingly popular. One method of reproducing the information stored on the microfilm comprises exposing the microfilm to light and projecting a light image onto an integral photoconductive copy paper, which paper comprises a highly electrically conductive layer with a photoconductive coating bonded directly to said electrically conductive layer on one side. Suitable copy papers of this type are described in US. Patent No. 3,010,884 to Johnson and Neher. After exposure of the photoconductive coating of the copy sheet to the light image, the light-struck areas become more electrically conductive than the background or no-n-light-struck areas. Selective electrolytic development of the light-struck areas can be accomplished with an electrolytic developer solution containing metal ions. Such solutions may be solutions of copper sulfate or silver nitrate, although other electrolytic developer materials have been provided. Apparatus adapted for use with copy paper of the above type is described in the above-referred to patent No. 3,011,963 to Johnson and Neher. The electrolytic electrophotographic apparatus comprises an exposure station including means for supporting microfilm, a lamp, a condensing lens system on one side of said film supporting means and an enlarging lens system on the opposite side, means supporting a supply roll of copy paper, means receiving and positioning a portion of the paper from the supply roll in the path of the light projected through the microfilm and a developing apparatus for electrolytically developing the latent image on the exposed copy paper.

The present invention relates to a novel apparatus for use with an exposure assembly for the development of the latent or differential conductive image imparted to the photoconductive copy paper and the preferred apparatus is illustrated in the drawing. The apparatus comprises a reservoir 1 adapted to contain :a quantity of the electrolytic solution 4, a pair of pumping rolls 2 and 3, and an electrode 5. The apparatus is used with a copy paper 6 having an electrically conductive backing 7 and photoconductive coating 8.

The reservoir 1 may be molded in one piece, to form a tray 'having a cross-section as illustrated, from a tough resistant plastic material such as an acetal resin, one suitable form of which is sold commercially under the trademark Delrin.

The pumping rollers 2 and 3 are positioned within the reservoir 1 and are adapted to be at least partially immersed in the electrolytic solution 4. The rollers 2 and 3 are rigid, of equal diameter and length, parallelly disposed and spaced apart a distance of between about 5 and about 25% of said diameter. The rollers may be formed Patented Feb. 21, 1967 of electrically insulating material but, as illustrated each of said rollers are formed by a stainless steel roller or core 9 having a smooth electrically insulating sleeve 10 of polymeric material such as polytetrafluoroethylene. Alternatively, the sleeve 10 may take the form of a coating of thermoset epoxy resin. The rollers 2 are mounted on axles 11 which are suitably bearinged in the end walls of the reservoir 1. The insulative sleeves 10 prevent current flow between the rollers 2 and 3 and the copy paper 6. If the rollers 2 and 3 have a length equal to or greater than the width of the copy paper 6 used therewith, solution is brought up to the edges of the paper and wets the electrically conductive backing and the current preferentially flows to the backing around the edges of the paper and sufficient current is then not available for electrolytic deposition. It is therefore preferred that the insulating pumping rollers 2 and 3 have a length slightly less than that of the copy paper to be used therewith to eliminate this flow of current about the edges of the paper. A pair of pumping rollers, which are about one-half inch shorter than the width of the copy paper to provide a spacing of about one-quarter inch at each end of the rollers 2 and 3, is considered satisfactory. Rough surface rollers could be used but smooth rollers are preferred as they minimize entrainment of air in the electrolytic solution. The roller 2 is driven by a suitable mechanical drive means, such as conventional motor 14, pulley and belt 16, and the two rollers are interconnected by suitable gearing, not shown, to drive roller 3 from roller 2. and afford counterrotation of the rolls as illustrated by the arrows in the drawing, wherein the direction of movement of the rolls adjacent the interstice is the same and upward. It is within the scope of this invention however, to have the rollers 2 and 3 driven at different rotational speeds and be of different size.

The rollers 2 and 3 are driven at a speed sufficient to afford a pumping action on the electrolytic solution 4. The solution is carried up on the surface of the rollers 2 and 3 as they are rotated to raise the solution to a position above the rollers and above the interstice between the same as shown in the drawing. For example, when one inch diameter rollers are used in the apparatus and are rotated at 1,600 revolutions per minute the rollers raise the solution as desired, forming the desired turbulent stream of solution which is forced into contact with the photoconductive coating on the unde-rsurface of the copy paper 6 disposed as shown in the drawing. The turbulent flow of the solution 4 is also carried over the rollers between each roller 2 and 3 and the cop-y paper 6 affording a large plating area as the paper is drawn across the developing apparatus. The speed of rotation can be adjusted for optimum efficiency and will vary, for example, with the viscosity of the developer solution, film speed, diameter of rollers, etc.

Means are provided for drawing the copy paper 6 across the apparatus in a predetermined spaced relation above the rollers 2 and 3. In the illustrated embodiment the means for transporting the copy paper comprises a pair of opposed contacting rollers 12 and 13 suitably journalled with respect to the apparatus to position the nip area of said rollers above the plane of the upper edges of the rollers 2 and 3. The rollers 12 and 13 are driven mechanically by conventional means such as a motor 17 and draw the paper from a supply roll, through an exposure area, and across the developing apparatus with sufficient tension to maintain the paper spaced a predetermined amount above the rollers 2 and 3 without contact there with, yet affording good contact with the turbulent stream of solution 4. The rollers 12 and 13 also serve to decrease the amount of solution which will be present on the copy when delivered therefrom to the operator.

The electric potential between the paper 6 and the solution 4 is provided from a suitable electrical source such as a battery, the positive terminal of which is connected to a thin flat electrode 5, which is immersed in the soluat essentially the same rotational speed tion 4 and disposed in and extending substantially the length of the bottom of the reservoir 1, and the negative terminal of which is connected to the conductive backing of the copy paper 6 through the roller 12 as shown or by other suitable means such as by connection at the supply roll supporting means. The electrode 5 and roller 12 thereby cause a current flow through the solution 4 and photoconductor 8 to the metal backing while the exposed surface of the copy paper 6 is in contact with said solution, thus electrolytically depositing suitable developer material from said solution onto said exposed electrically conductive surface to effect a visible image producing color change on said exposed surface corresponding to the original light image.

Referring now to FIGURE 2 there is illustrated a mechanical inspector apparatus 18 for inspecting mechanical parts. The apparatus 18 comprises a lamp and lens housing 19 which will project a collimated beam of light, as shown at 20, therefrom toward a work table 21 adapted to support the part. The part, while supported on the work table 21, is adjusted so that an enlarged image of the part, produced by a magnifying lens and projecting lens 22, either in silhouette or in a face view is projected onto a groundglass viewing screen 23, when an intermediate movable mirror 24 is positioned as shown in dotted lines in FIGURE 2. For purposes of keeping inspection records, and for transmitting the results to others, it is often desirable to copy the image obtained. This is accomplished in the illustrated device by incorporating into the inspecting apparatus 1-8 a device for electrolytically reproducing an image which device comprises an exposure station or area 25, a developing station 26 and means for supporting and conveying the photoconductive copy paper through said stations to an exit and tearotf area 27. The supporting and conveying means comprises a spindle 28 on which is supported a supply roll 29 of the copy paper 30; a pair of guide rollers 31 and 32, the open area therebetween being the exposure area 25; and a pair of feed rollers 33 and 34 which are in the developing station and which maintain .the copy paper 30 in proper position in the same manner as the corresponding rollers 12 and 13 illustrated in FIGURE 1. The feed rollers 33 and 34 direct the developed copy paper toward the exit area 27. The exposure onto the photoconductive copy paper 30 between guide rollers 31 and 32 is made possible by raising the mirror 24 to the solid line position shown, by suitable lever means (not shown), and reflecting the light image from a large fixed mirror 35 positioned in the bottom portion of the inspector 18 onto the copy paper.

The developing station 26 comprises a developing apparatus as shown in FIGURE 1, having a pair of rotatably driven, spaced, parallel, similar pumping rollers which force a stream of liquid electrolytic solution against the copy paper to develop the areas light-struck in the exposure station before the paper is fed out through the exit area 27. Suitable means may be used to make the inspecting machine 18 automatic to produce a copy of the part after a switch, button etc. (not shown) is actuated to initiate operation of said means.

Developing apparatus of this general type employed in machines as illustrated are normally operated only intermittently. Under such conditions, systems using a gelatin or sponge covering on the solution applying roller are very difficult to keep clean. The apparatus of this invention using smooth rollers is easily cleaned as the solution drains from the rollers after their rotation is stopped. This is especially true when polytetrafiuoroethylene coated rollers are used. The small amount of solution which may remain in the form of a meniscus between the rollers 2 and 3 and the paper 6 is avoided by stopping the rotation of the pumping rollers 2 and 3 before the rotation of the paper transport rollers 12 and 13 stops.

The present developing apparatus has the advantage of maintaining sufficient fresh solution in contact with the paper to give good ion replenishment and flush the plating area of gas bubbles and residue, providing more eflicient development with a minimum contact time. Additionally, the flow of solution maintains a lower temperature in the developing area resulting in a better print with improved density and evenness of copy. When the tempertaure is allowed to build up in the developing area the electrical conductivity of the'coating 8 is substantially impaired reducing the quality of the image.

It is to be understood that the substitutions of materials and rearrangement of parts which may become apparent to one having ordinary skill in the art are contemplated as coming within the scope of this invention.

Having thus described the invention, what is claimed is:

1. An apparatus for electrolytic development of an image pattern comprising a shallow tray adapted to receive a supply of electrolytic developer solution, a pair of rotatably supported rollers disposed in parallel spaced relation within said tray and adapted to be at least partially immersed in said solution, drive means for rota-ting said rollers in opposite directions to effect therebetween an upward pumping action on said solution lifting the same to provide a turbulent stream of said solution flowing above said rollers, an electrode disposed in said solution, and means for drawing an electrolytically developable photoconductive copy paper across said tray in vertically spaced relation to said rollers such that the photoconductive surface of the paper contacts the stream of developer solution as the paper is drawn across said tray and a high resistance electrical path is formed between the paper and said rollers.

2. An apparatus for electrolytic development of an image pattern comprising a shallow tray adapted to receive a supply of electrolytic developer solution, a pair of rigid, electrically insulated, rotatably supported rollers disposed in parallel spaced relation within said tray and adapted to be at least partially immersed in said solution, drive means for rotating said rollers in opposite directions at a relatively rapid rate :to efiect a pumping action on said solution lifting a portion thereof and affording a turbulent flow of said solution in the area above said rollers, an electrode disposed in said solution, and means for drawing a web of electrolytically developable photoconductive paper across said tray in vertically spaced relation to said rollers and at a slower linear speed-than the peripheral velocity of any one point on the rollers, such that the photoconductive surface of the web comes in contact with the flow of the developer solution as the web is drawn across said tray.

3. An apparatus for electrolytic development of an image pattern comprising a shallow tray adapted to receive a supply of electrolytic developer solution, a pair of electrically insulated, rotatably supported, equal-diameter rollers disposed within said tray in parallel relation and spaced apart a distance of between about and about 25% of said diameter and adapted to be at least partially immersed in said solution, drive means for rotating said rollers in opposite directions at a relatively rapid rate to effect a pumping action on said solution lifting a portion thereof and afiiording a turbulent flow of said solution in the area above said rollers, an electrode disposed in said solution, and means for drawing a web of electrolytically developable photoconductive paper across said tray in spaced relation to said rollers and at a slower linear speed than the peripheral velocity of any one point on the rollers, such that the photoconductive surface of the web comes in contact with the flow of the developer solution as the web is drawn across said tray.

4. In an electrolytic image copying machine having an exposure station for exposing photoconductive copy paper, which comprises a photoconductive coating on an electrically conductive backing, a developing station, and means for drawing said exposed copy paper through said developing station, the improvement comprising a pair of rollers in said developing station for maintaining a stream of electrolytic solution in contact with the coating on said paper as the same is drawn therethrough, drive means for said rollers, reservoir means adapted to contain electrolytic solution in which said rollers are to be at least partially immersed, electrode means positioned in the electrolytic solution and wetted thereby affording an electrical potential between said solution and said conductive backing, means maintaining said coated surface of said copy paper in contact with said stream of solution and out of contact with said pair of rollers, and said rollers and said paper being spaced and constructed such that current flow between said paper and rollers is limited.

5. An apparatus as described in claim 2 wherein said rollers are similar and of uniform diameter and have a smooth outer surface and have a length less than the width of the copy paper.

6. An apparatus as described in claim 2 wherein said rollers have an outer covering of polytetrafluoroethylene.

7. The method of developing electrolytically an image pattern formed on a photoconductive copy paper after exposure thereof to a light-image a photoconductive copy paper, comprisingthe steps of feeding the exposed sheet of photoconductive copy paper across and in vertical spaced relation to a reservoir containing a supply of electrolytic solution, rotating a pair of parallel spaced rollers partially immersed in said solution to pump the same upwardly in a turbulent stream having a contracting relationship with a large exposed surface area of the copy paper while impressing an electric potential between said paper and said solution for electrolytic deposition from the electrolytic solution on said copy paper to afford development of a visible image pattern on said copy paper which is free from streaks.

References Cited by the Examiner UNITED STATES PATENTS 2,271,736 2/ 1942 Hall 204-206 3,011,963 12/1961 Johnson 204-18 3,203,395 8/1965 Liller 11793.4

FOREIGN PATENTS 367,567 1/ 1923 Germany.

JOHN H. MACK, Primary Examiner. T. TUFARIELLO, Assistant Examiner. 

7. THE METHOD OF DEVELOPING ELECTROLYTICALLY AN IMAGE PATTERN FORMED ON A PHOTOCONDUCTIVE COPY PAPER AFTER EXPOSURE THEREOF TO A LIGHT-IMAGE A PHOTOCONDUCTIVE COPY PAPER, COMPRISING THE STEPS OF FEEDING THE EXPOSED SHEET OF PHOTOCONDUCTIVE COPY PAPER ACROSS AND IN VERTICAL SPACED RELATION TO A RESERVOIR CONTAINING A SUPPLY OF ELECTROLYTIC SOLUTION, ROTATING A PAIR OF PARALLEL SPACED ROLLERS PARTIALLY IMMERSED IN SAID SOLUTION TO PUMP THE SAME UPWARDLY IN A TURBULENT STREAM HAVING A CONTRACTING RELATIONSHIP WITH A LARGE EXPOSED SURFACE AREA OF THE COPY PAPER WHILE IMPRESSING AN ELECTRIC POTENTIAL BETWEEN SAID PAPER AND SAID SOLUTION FOR ELECTROLYTIC DEPOSITION FROM THE ELECTROLYTIC SOLUTION ON SAID COPY PAPER TO AFFORD DEVELOPMENT OF A VISIBLE IMAGE PATTERN ON SAID COPY PAPER WHICH IS FREE FROM STREAKS. 